The chemical sensitization of colloid-silver halide photographic emulsions by a variety of compounds used either alone or in combination has been well documented as shown in Mees-James, "The Theory of The Photographic Process", 1966, the Macmillan Company, Chapter 3 and Chapter 5. Perhaps the oldest and most commonly used method of sensitization is by the addition to a photographic emulsion of a compound which will provide labile sulfur to the silver halide system. It is with this type of sensitization that the present invention is primarily concerned.